1. Field Of The Invention And Contract Statement
The invention relates to a method for removing halogenated aliphatic and aromatic compounds from petroleum products and more particularly to a method for removing polychlorinated biphenyl from petroleum products.
2. Discussion Of Background And Prior Art
The physical and chemical properties of polychlorinated biphenyls (PCBs) made them attractive for a broad spectrum of applications. In general, the chlorinated, aromatic compounds have excellent chemical, thermal stability and dielectric properties. In particular, the polychlorinated biphenyls are very stable compounds. The PCBs are generally chemically inert and are nonreactive under ordinary circumstances, and consequently, only extreme reagents and reaction conditions form new compounds.
Consequently, the polychlorinated biphenyls have been used as electrical insulating fluids for transformer and capacitors and as industrial fluids for machining coolants, hydraulic systems and vacuum pumps. The PCBs are also applicable as fire retardants, heat transfer agents and plasticizers.
Unfortunately, some of the properties responsible for the broad spectrum of applications of PCBs are also the reason for the health and environmental problems recently associated with polychlorinated biphenyls. The PCB class of compounds is very toxic to living cells, is toxic in small amounts and has systemic toxic effects. Relatively recent investigations have indicated that the PCBs are possibly carcinogenic and induce neoplastic changes in rats.
The polychlorinated biphenyls have accumulated in food chains because of their solubility in fatty tissue and resistance to chemical degration. Basically, the problems attendant with PCBs is that the toxic PCBs are fat soluble, are stored in the lipids of animals and tend to be concentrated in amounts high in the food chain. Also, the resistance of PCBs to thermal, chemical and biological degradation has constributed to the accumulation of the PCBs in particular in industrial environments. The very slow biodegradation rates and considerable resistance to metabolic changes of PCBs makes them almost a ubiquitous environmental problem and contaminant. Consequently, the Environmental Protection Agency (EPA) has severely limited the use of polychlorinated biphenyls and placed stringent restrictions on the disposal of them.
Oils and other organic liquids containing low levels, e.g., less than 10,000 ppm. of polychlorinated biphenyls present considerable disposal problems. Incineration is the only disposal method and currently approved by EPA. Equipment and operational costs for incineration of oils and the like containing low levels of PCB are excessive. The PCBs are usually destroyed by incineration at high temperatures, that is, greater than 1100.degree. C., with long residence time in the incinerators. Ordinary incinerators used to dispose of organic matter normally will tend to vaporize the PCBs instead of converting them to carbon dioxide, water and hydrogen chloride. So an economical and continuous process is needed for concentrating the polychlorinated biphenyls in a small amount of liquid (for subsequent incineration) while purifying the contaminated liquids for further use or separate disposal.
Solvent extraction, distillation and evaporation have been used for separating liquids, concentrating materials in liquids and removing impurities from liquids. The petroleum companies use solvent extraction for adjusting viscosity, controlling impurities and other reasons. Several processes are described in Hess, L. Y., "Reprocessing and Disposal of Waste Petroleum Oils," Noyes Data Corp., (1979). Methods of analysis for polychlorinated biphenyls, including solvent extraction and other analytical techniques, are described in Hutzinger, O., et al., "The Chemistry of PCB's." CRC Press Inc., Fourth Printing, (1980).